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The fact that electric arc could operate was known for over a 100 years. The first ever underwater welding was carried out by British Admiralty – Dockyard for sealing leaking ship rivets below the water line. Underwater welding is an important tool for underwater fabrication works. In 1946, special waterproof electrodes were developed in Holland by ‘Van der Willingen’. In recent years the number of offshore structures including oil drilling rigs, pipelines, platforms are being installed significantly. Some of these structures will experience failures of its elements during normal usage and during unpredicted occurrences like storms, collisions. Any repair method will require the use of underwater welding.

CLASSIFICATION

Underwater welding can be classified as
1) Wet Welding
2) Dry Welding

In wet welding the welding is performed underwater, directly exposed to the wet environment. In dry welding, a dry chamber is created near the area to be welded and the welder does the job by staying inside the chamber.

WET WELDING

Wet Welding indicates that welding is performed underwater, directly exposed to the wet environment. A special electrode is used and welding is carried out manually just as one does in open air welding. The increased freedom of movement makes wet welding the most effective, efficient and economical method. Welding power supply is located on the surface with connection to the diver/welder via cables and hoses.

Principle of operation
The process of underwater wet welding takes in the following manner:

The work to be welded is connected to one side of an electric circuit, and a metal electrode to the other side. These two parts of the circuit are brought together, and then separated slightly. The electric current jumps the gap and causes a sustained spark (arc), which melts the bare metal, forming a weld pool. At the same time, the tip of electrode melts, and metal droplets are project and implimentationed into the weld pool. During this operation, the flux covering the electrode melts to provide a shielding gas, which is used to stabilize the arc column and shield the transfer metal. The arc burns in a cavity formed inside the flux covering, which is designed to burn slower than the metal barrel of the electrode.

Underwater welding was invented by the Russian metallurgist Konstantin Khrenov in 1932.
The first ever underwater welding was carried out by British Admiralty – Dockyard for sealing leaking ship rivets below the water line.
Underwater welding is an important tool for underwater fabrication works.

CLASSIFICATION

Underwater welding can be classified as-
1) Wet Welding
2) Dry Welding
In wet welding the welding is performed underwater, directly exposed to the wet environment. In dry welding, a dry chamber is created near the area to be welded and the welder does the job by staying inside the chamber.

WET WELDING

Wet Welding indicates that welding is performed underwater, directly exposed to the wet environment. A special electrode is used and welding is carried out manually just as one does in open air welding. The increased freedom of movement makes wet welding the most effective, efficient and economical method.

Dry welding

Dry welding is carried out in chamber sealed around the structure to be welded.
The chamber is filled with a gas (commonly helium containing 0.5 bar of oxygen) at the prevailing pressure.
The habitat is sealed onto the pipeline and filled with a breathable mixture of helium and oxygen, at or slightly above the ambient pressure at which the welding is to take place.
This method produces high-quality weld joints.
The gas tungsten arc welding process is employed for this process.

Advantages

Welder/Diver Safety – Welding is performed in a chamber, immune to ocean currents and marine animals.

Good Quality Welds – This method has ability to produce welds of good quality.

Disadvantages

The habitat welding requires large quantities of complex equipment and much support equipment on the surface. The chamber is extremely complex.
Cost of habitat welding is extremely high and increases with depth.

Future of Underwater welding

Automation of the underwater welding. Present trend is towards automation to develop a technology, where diver performs pipefitting, installs the trac and the rest process is automated.

Welding is an unavoidable process of modern engineering – civil, electrical, mechanical, automobiles, marine aeronautical – in all branches. It is used in fabrications and erections in infrastructures and installations. It joins metals or thermoplastics. Forming a pool of molten mass – the weld puddle – and allowing it to cool to become a strong joint is the basis of the process of welding. For repairing to be carried out underwater, there is a separate process. That is called underwater welding. If damaged ships are to be repaired, underwater welding is the basic technology to be used. It is a highly-specialized profession – more employed in the oil or shipping industry and also in the defense operations.

Wet welding:

In the case of wet welding, the operation is completed under water, directly exposed to the wet environment. For this purpose, a different type of electrode is used. The function is carried out manually. The welder is allowed to have freedom of movement. Hence, wet welding is the most effective, efficient and economical process.

The welding power and supply unit is placed on the surface and is connected to the welder with the help of cables and hoses.

The Advantages:
* The expenditure is very minimal. Unlike in the case of dry welding.
* The speed of the operation is extremely high.
* As the equipments are very minimum, the welding can be performed in a shorter time with minimal planning. The Disadvantages:
* The weld is quenched is very fast under water. It decreases the ductility and impact strength an also makes the weld very porous.
* The visibility of the welder is not up to the required level.
* The amount of voltage that can b employed is very limited. Care has to be taken so that the welder is not harmed by probable electrical shocks.

Dry Welding:

In case of dry welding, otherwise known as Hyperbaric welding, the whole operation is completed in a chamber, sealed around the structure to be welded. The chamber is filled with gas – normally helium – containing 0.5 bar oxygen. The chamber is fitted onto the pipeline and is filled with the breathable mixture of air. The operation is carried out in higher pressure. The gas tungsten arc welding process is used.The Advantages:
* Welding can be carried out without getting affected by ocean currents and marine animals.
* Better quality welds can be used.
* From the surface itself, there is a possibility of visually monitoring joint preparation and pipe alignment. The Disadvantages:
* The chamber is very complex. Large support equipment is needed at the surface to support the chamber.
* The expense will be very high. The cost increases proportionately to the depth under water.
* The chamber has limited reusability.